From 30fcc21d8b093625ee30d2f9595f51429780eedd Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@pdimov.com>
Date: Sat, 14 Oct 2017 02:53:38 +0300
Subject: [PATCH] Add mp_cond

---
 include/boost/mp11/utility.hpp | 25 ++++++++++++++++++++
 test/Jamfile                   |  2 ++
 test/mp_cond.cpp               | 42 +++++++++++++++++++++++++++++++++
 test/mp_cond_sf.cpp            | 43 ++++++++++++++++++++++++++++++++++
 4 files changed, 112 insertions(+)
 create mode 100644 test/mp_cond.cpp
 create mode 100644 test/mp_cond_sf.cpp

diff --git a/include/boost/mp11/utility.hpp b/include/boost/mp11/utility.hpp
index f82d613..5935e6d 100644
--- a/include/boost/mp11/utility.hpp
+++ b/include/boost/mp11/utility.hpp
@@ -107,6 +107,31 @@ template<bool C, class T, template<class...> class F, class... U> using mp_eval_
 template<class C, class T, template<class...> class F, class... U> using mp_eval_if = typename detail::mp_eval_if_c_impl<static_cast<bool>(C::value), T, F, U...>::type;
 template<class C, class T, class Q, class... U> using mp_eval_if_q = typename detail::mp_eval_if_c_impl<static_cast<bool>(C::value), T, Q::template fn, U...>::type;
 
+// mp_cond
+
+// so elegant; so doesn't work
+// template<class C, class T, class... E> using mp_cond = mp_eval_if<C, T, mp_cond, E...>;
+
+namespace detail
+{
+
+template<class C, class T, class... E> struct mp_cond_impl;
+
+} // namespace detail
+
+template<class C, class T, class... E> using mp_cond = typename detail::mp_cond_impl<C, T, E...>::type;
+
+namespace detail
+{
+
+template<class C, class T, class... E> using mp_cond_ = mp_eval_if<C, T, mp_cond, E...>;
+
+template<class C, class T, class... E> struct mp_cond_impl: mp_defer<mp_cond_, C, T, E...>
+{
+};
+
+} // namespace detail
+
 // mp_quote
 template<template<class...> class F> struct mp_quote
 {
diff --git a/test/Jamfile b/test/Jamfile
index 54968ae..1f85aeb 100644
--- a/test/Jamfile
+++ b/test/Jamfile
@@ -90,6 +90,8 @@ run mp_quote.cpp ;
 run mp_invoke.cpp ;
 run mp_invoke_sf.cpp ;
 run mp_quote_trait.cpp ;
+run mp_cond.cpp ;
+run mp_cond_sf.cpp ;
 
 # integer_sequence
 run integer_sequence.cpp ;
diff --git a/test/mp_cond.cpp b/test/mp_cond.cpp
new file mode 100644
index 0000000..08a625f
--- /dev/null
+++ b/test/mp_cond.cpp
@@ -0,0 +1,42 @@
+
+// Copyright 2017 Peter Dimov.
+//
+// Distributed under the Boost Software License, Version 1.0.
+//
+// See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt
+
+
+#include <boost/mp11/utility.hpp>
+#include <boost/mp11/integral.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <type_traits>
+
+int main()
+{
+    using boost::mp11::mp_cond;
+    using boost::mp11::mp_true;
+    using boost::mp11::mp_false;
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_cond<mp_true, char[]>, char[]>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_cond<mp_true, char[], void>, char[]>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_cond<mp_true, char[], void, void>, char[]>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_cond<mp_true, char[], void, void, void>, char[]>));
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_cond<mp_false, int, mp_true, char[]>, char[]>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_cond<mp_false, int, mp_true, char[], void>, char[]>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_cond<mp_false, int, mp_true, char[], void, void>, char[]>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_cond<mp_false, int, mp_true, char[], void, void, void>, char[]>));
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_cond<mp_false, int, mp_false, float, mp_true, char[]>, char[]>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_cond<mp_false, int, mp_false, float, mp_true, char[], void>, char[]>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_cond<mp_false, int, mp_false, float, mp_true, char[], void, void>, char[]>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_cond<mp_false, int, mp_false, float, mp_true, char[], void, void, void>, char[]>));
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_cond<mp_false, int, mp_false, float, mp_false, double, mp_true, char[]>, char[]>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_cond<mp_false, int, mp_false, float, mp_false, double, mp_true, char[], void>, char[]>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_cond<mp_false, int, mp_false, float, mp_false, double, mp_true, char[], void, void>, char[]>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_cond<mp_false, int, mp_false, float, mp_false, double, mp_true, char[], void, void, void>, char[]>));
+
+    return boost::report_errors();
+}
diff --git a/test/mp_cond_sf.cpp b/test/mp_cond_sf.cpp
new file mode 100644
index 0000000..c1bb4de
--- /dev/null
+++ b/test/mp_cond_sf.cpp
@@ -0,0 +1,43 @@
+
+// Copyright 2017 Peter Dimov.
+//
+// Distributed under the Boost Software License, Version 1.0.
+//
+// See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt
+
+
+#include <boost/mp11/utility.hpp>
+#include <boost/mp11/integral.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <type_traits>
+
+int main()
+{
+    using boost::mp11::mp_cond;
+    using boost::mp11::mp_true;
+    using boost::mp11::mp_false;
+    using boost::mp11::mp_valid;
+
+    BOOST_TEST_TRAIT_FALSE((mp_valid<mp_cond>));
+
+    BOOST_TEST_TRAIT_FALSE((mp_valid<mp_cond, mp_true>));
+    BOOST_TEST_TRAIT_FALSE((mp_valid<mp_cond, mp_false>));
+
+    BOOST_TEST_TRAIT_TRUE((mp_valid<mp_cond, mp_true, void>));
+    BOOST_TEST_TRAIT_TRUE((mp_valid<mp_cond, mp_true, void, void>));
+
+    BOOST_TEST_TRAIT_FALSE((mp_valid<mp_cond, mp_false, void>));
+    BOOST_TEST_TRAIT_FALSE((mp_valid<mp_cond, mp_false, void, void>));
+
+    BOOST_TEST_TRAIT_FALSE((mp_valid<mp_cond, mp_false, void, mp_true>));
+    BOOST_TEST_TRAIT_TRUE((mp_valid<mp_cond, mp_false, void, mp_true, void>));
+
+    BOOST_TEST_TRAIT_FALSE((mp_valid<mp_cond, mp_false, void, mp_false>));
+    BOOST_TEST_TRAIT_FALSE((mp_valid<mp_cond, mp_false, void, mp_false, void>));
+
+    BOOST_TEST_TRAIT_FALSE((mp_valid<mp_cond, mp_false, void, mp_false, void, mp_true>));
+    BOOST_TEST_TRAIT_TRUE((mp_valid<mp_cond, mp_false, void, mp_false, void, mp_true, void>));
+
+    return boost::report_errors();
+}